Telegraph system



May 29, 1934. J. I. BELLAMY TELEGRAPH SYSTEM Filed- Nov. 28, 1930 2 Sheets-Sheet 1 LINE WEST LINE EAST LINE EAST LINE wsar L/NE EAST May 29, 1934- J. l. BELLAMY TELEGRAPH SYSTEM 2 Sheets-Sheet 2 Filed Nov. 28, 1930 3 8 v IF IF ww \w\ 3 E m v Q mw g u i -Im. en DIP- Jul-m LEsZZam Patented May 29, 1934 UNITED STATES 1,960,569 TELEGRAPH SYSTEM" John I. Bellamy, Brookfleld, Ill.,

assignor, by

mesne assignments, to Associated Electric Laboratorics, Delaware Inc., Chicago, 111., a corporation of Application November 28, 1930, SerialNo. 498,541 19 Claims. (CL 178-71) The present invention relates in general to telegraph systems. The main object of the invention is the production of an improved telegraph system employing vacuum tubes both in the two-way telegraph repeaters and at the end and Way stations.

According to one feature of the invention, the improved system eliminates the use of inductive devices at the stations and in the repeaters, and provides practically a pure resistance circuit thereby permitting more rapid signal transmission.

According to another feature of the invention, the necessity of holding coils or holding relays in the two-way repeaters is eliminated as the holding function is performed by the vacuum tubes.

The above and other features of the invention will become apparent upon a further perusal of the specification'in connection with the accompanying drawings forming a part thereof and comprising Figs. 1 to 4, inclusive. These drawings show by means of the usual circuit diagrams several modifications of two-way telegraph repeaters employing vacuum tubes, and a complete telegraph system showing the preferred embodiment of the present invention.

Referring now particularly to the drawings, Fig. 1 shows a two-way telegraph repeater suitable for use in connection with the standard telegraph systems in which inductive devices are connected in the line circuits at the telegraph stations. Associated with the line relays and are the holding coils 6 and 11, respectively. The mechanical arrangement between the holding coils and their associated line relays is fully disclosed in my prior co-pending application, Serial No. 322,631, filed November 30, 1928.

Fig. 2 discloses a. two-way repeater similar to that disclosed in Fig. 1 except that the holding coils of Fig. 1 have been eliminated and two holding tubes have been provided to hold the respective line relays operated during the repeating of telegraph signals.

The repeater shown in Fig. 3 of the drawings is a further development in which the holding tubes have been eliminated and in which the line or repeating tube also performs the holding function.

Fig. 4 of the drawings discloses an-end station S1, a way station S2, and a two-way repeater R of an improved telegraph system employing only resistances in the line circuit and employing vacuum tubes at the end and way stations and also at the two-way telegraph repeaters.

Referring now particularly to Fig. 1 of the drawings, the operation of the apparatus disclosed therein will be explained. The line east and line west, 1 and 2, respectively, are normally connected at the distant ends to the positive pole of a. line battery, such as 18, and line current is therefore normally flowing through the inductive coils 16 and 22. The voltage drops across these coils overcome the effect of the negative biasing batteries 17 and 23 and the normal potential on the grid of tubes 3 and 4 is sufilciently positive with respect to the filament to allow plate current to flow and maintain the line relays 5 and 10 in operated position.

It will be assumed that a telegraph message F is to be transmitted from a distant station over line 1. When the switch associated with the key at the sending station is opened, line current ceases to flow through coil 16 and the negative biasing battery 17, assisted by the induced E. M. F.

in the winding of coil 16 due to the interruption of current, places a negative potential on the grid of tube 3, thereby stopping the flow of plate current and allow relay 5 to release. In releasing, line relay 5 at armature 8 opens the line 2 thereby causing the sounders at all stations on this line to release. The opening of line 2 affects tube 4 in the same manner as the opening of line 1 affected tube 3. However, at the same time, the normally closed shunt around the winding of holding coil 11 is opened at armature 7 and this holding coil is energized'from ground,

winding of holding coil 11, resistance 14, to battery 15. The holding coil 11 maintains armatures 12 and 13 of line relay 10 in operated position to prevent the opening of the incoming line. Each time the telegraph key at the sending station is closed in accordance with the call letters of the wanted station, the RI drop across coil 16 due to the flow of line current again overcomes the effect of battery 17 and places the grid of tube 3 at a positive potential with respect to the filament. The resulting plate current again operates relay 5 which closes the outgoing line at armature 8 to repeat the signals. During the intervals when relay 5 is released the shunt is removed from holding coil 11 and this coil is energized to maintain the incoming line closed. When relay 5 is energized to repeat the signals the outgoing line is closed and the RI drop across coil 22 renders the tube 4 operative to hold relay 10 energized. Relay 10 at armature 13 maintains the incoming line closed.

When the operator at the wanted station hears the call letters of his station, he opens the switch associated with his telegraph key,,thereby causing a break in line 2. The next time relay 5 energizes to repeat a signal, the line 2 will be open at the answering station and accordingly no line current will flow to render tube 4 operative. Since the winding of holding coil 11 is shunted at armature '7 of relay 5 and since relay 10 is not energized, the armatures 12 and 13 will restore to normal. At armature 12, the shunt is removed from holding coil 6 and this coil energizes to maintain armatures 7 and 8 in operated position, while at armature 13 the incoming line 1 is opened. The operator at the sending station no longer hears his sounder responding to the operations of the key since the line is permanently opened at the repeater, and he knows that the operator at the wanted station has answered. He then closes his switch and waits for the go ahead signal of the answering station. When the answering operator has sent the go ahead signal he again closes his switch. The sending operator, upon receiving this signal, opens his switch and proceeds with the sending of the message.

At any time during the transmission of a message the receiving operator may break his line, as disclosed in the foregoing, as for example if he has missed part of the message. The opening of the line 2 at the receiving station results in the opening of line 1 at the repeater in the manner described above. When the sending operator notes that his sounder is not responding to the operations of the key, he closes his switch and waits to hear from the receiving operator.

Similarly, if the operator at a station on line 2 desires to transmit a message to a station on line 1, he opens the switch associated with his telegraph key, thereby stopping the flow of current through coil 22. Biasing battery 23 becomes effective to make tube 4 inoperative and relay 10 releases to open line 1 at armature 13. At the same time the shunt around holding coil 6 is removed at armature 12 and this coil energizes to maintain armatures 7 and 8 in operated positions. Each time the key at the sending station is closed in accordance with the call letters of the wanted station or the telegraph message, line relay 10 energizes to repeat the signal over line 1 at armature 13 and at armature 12 again shunts holding coil 6. However, the incoming line 2 is held closed since, with line 1 closed, the tube 3 is effective to hold relay 5 energized during the intervals when holding coil 6 is shunted. The operator at the receiving station may break in at any time by opening his switch. The next time relay 10 energizes and closes armature 12 to shunt the holding coil 6, armatures 7 and 8 restore to normal since, the outgoing line 1 being open at the receiving station, there is no" line current flowing to render tube 3 operative and relay 5 does not energize. The sending operator upon noting that his sounder is no longer responding to the operations of the key, closes his switch and waits to hear from the receiving operator.

In the modification shown in Fig. 2 of the drawings, the holding arrangement including the hold ing coils 6 and 11 of Fig. 1 is replaced by an arrangement employing the holding tubes 27 and 28. Normally with the lines 25 and 26 closed,-

the voltage drops across coils 31 and 32 overcome the effect of the biasing batteries 44 and 34, respectively, and maintain the grids of tubes 29 and 30 at a positive potential, allowing plate current to flow in the plate circuits of these tubes.

The line or repeating relays 35 and 40 are, therefore, normally maintained in operated position. Armature 36 of relay35 connects the negative pole of battery 38 to the grid of theholding tube 28 to prevent any flow of current in the plate circuit of this tube, and armature 41 of line relay 40 connects the negative pole of battery 38 to the grid of tube 2'7 'to .maintain the grid of this tube at a negative potential and prevent a flow of current in its plate circuit. Thus the holding tubes 27 and 28 are normally inoperative while the repeating tubes 29 and 30 serve to maintain the repeating relays 35 and 40 in operated position.

When the operator at a station on line 25 opens the switch associated with his key preparatory to sending a message, positive battery is disconnected from line 25 and the flow of line current through coil 31 ceases, allowing the biasing battery 44 to become eiiective. In addition, the sudden interruption of current flow through the inductive winding 31 induces an E. M. F. in this winding which assists the biasing battery 44 and places a high negative potential on the grid of tube 29.

Plate current ceases to flow through the repeating relay 35 and this relay, therefore, releases, opening the outgoing line 26 at armature 3'7, and disconnecting the negative pole of battery 38 from the grid of tube 28 at armature 36.. The biasin battery 49 of tube 28 is not of sufliciently high voltage to stop the flow of current in the plate circuit of the tube but is provided to bias the tube so that the proper amount of plate current will flow through the repeating relay 40. Accordingly when armature 36 releases and opens the connection from the negative pole of battery 38 to the grid of tube 28, a plate current flows through repeating relay 40, maintaining this relay in operated position to hold the incoming line closed. Each time the key at the sending station is closed in accordance with the call letters of the wanted station or the telegraph message, current flow through coil 31 renders tube 29 effective to operate relay 35. At armature 3'7, relay 35 closes the outgoing line to repeat the signal and at armature 36 it connects the battery 38 to the grid of holding tube 28, rendering this tube inoperative. However, the closure of the outgoing line allows line current to flow and the RI drop across coil 32 again allows tube 30 to become operative to energize relay 40. The incoming line is thereby maintained closed. Should the receiving operator desire to interrupt to answer his station call or to ask for a repetition of a portion of the message, he opens the switch associated with his key, thereby opening the line 26. If the key at the sending station is open at this time, nothing happens since line 26 will also be open at contacts 37. However when repeating relay 35 energizes to repeat the next signal, battery 38 is again connected to the grid of tube 28 to render this tube inoperative. Tube 30 is also maintained inoperative since the line is open at the receiving station and there is no current flow through coil 32. Relay 40, therefore, releases and opens the incoming line at contacts 42 and disconnects battery 38 from the grid of tube 2'7 at contacts 41. Tube 2'1 becomes operative to hold the relay 35 energized. The sending operator will be informed of the break by the receiving operator by the failure of his sounder to respond to the operations of the key. He thereupon closes his switch and waits to hear from the receiving operator.

Similarly, when a distant station is transmitting telegraph signals over line 26, each closure of the key at the sending station results in a positive potential on the grid oi tube 30 due to the RI drop across coil 32. The resulting plate current operates repeating relay 40 which repeats the signal over the outgoing line 25 at armature 42. At armature 41, relay 40 closes the connection from the negative pole of battery 38 to the grid oi. holding tube 27, stopping the flow of current in the plate circuit of this tube. However, with the outgoing line closed,,the tube 29 is effective to maintain relay 35 energized.

To summarize the foregoing, in repeating from east to west, the repeating tube 29 is rendered operative each time the key at the sending station is closed, and operates relay 35 in accordance with the telegraph signal. Relay 35 repeats the impulses by closing the outgoing line at contacts 37. The holding tube 28 is rendered inoperative by the closure of contacts 36, but relay 40 is maintained energized by the repeating tube 30 which is rendered operative by the voltage drop across coil 32. Similarly, in transmitting signals from west to east, the tube 30 is rendered operative each time the key at the sending station is closed, and operates the repeating relay 40 in accordance with the telegraph signal. Relay 40 repeats the signals over the outgoing line 25 by closing contacts 42. The closing of contacts 41 renders holding tube 27 inoperative, but relay 35 is now held energized by tube 29, which was rendered operative by the flow of line current through coil 31. The receiving operator in either case can break .in at any time by opening the switch associated with his telegraph key.

In the modification shown in Fig. 3 of the drawings, the holding tubes 27 and 28 of Fig. 2 have been eliminated and the line tubes 52 and 53 perform both the repeating and holding functions. Normally, with the line circuits closed, the biasing batteries 68 and 71 are inefi'ective due to the voltage drops across coils 58 and 59 and current flows in the plate circuits of tubes 62 and 63 to maintain relays 55 and 60 operated. When the operator at a station on line opens his switch preparatory to sending a message, current ceases to fiow through coil 58 and the battery 68 becomes eiTective to place a negative potential on the grid of tube 52, thereby stopping the flow of plate current through relay 55. Relay releases and opens the outgoing line at contacts 57. At contacts 56 it removes the normal short-circuit from battery 70 and resistance 69. This battery maintains a positive potential on the grid of tube 53 after line current ceases to flow through the coil 59 and there is no longer a voltage drop across this coil to overcome the biasing battery 71. Relay is thereby held energized by tube 53 and the incoming line is maintained closed at contacts 62.

Each time the key at the sending station is closed in accordance with thecall letters of the wanted station or the telegraph message, the line current through coil 58 again produces a voltage drop across the coil which overcomes the effect of battery 68 and makes the grid of tube 52 positive with respect to the filament. The resulting plate current operates relay 55 which repeats the telegraph signal over the outgoing line at contacts 57. At contacts 56, the battery and resistance 69 are short-circuited but tube 53 is maintained operative at this time by the voltage drop across coil 59 since the outgoing line is now closed. The operator at the receiving station can break in at any time to answer his station call or to ask for a repetition of a portion of the message it he fails to get it properly, by simply opening the switch associated with his telegraph key. If line relay 55 is deenergized at this time nothing happens since battery 70 maintains tube 53 operative to hold relay 60 energized. When relay 55 energizes to repeat the next signal, battery 70 is short-circuited and, since there is no current flow through coil 59, battery 71 becomes effective to place a negative potential on the grid of tube 53, thereby causing relay 60 to release and open the incoming line at contacts 62. When the sending operator observes that his sounder is no longer responding to the operations of his sending key, he closes his switch and waits to hear from the receiving operator.

Signals from west to east are repeated in a similar manner. Each time the sending operator closes his key, current flow through coil .59 renders tube 53 operative to energize relay 60. Relay 60 repeats the signal by closing contacts 62 and short-circuits battery 67 and resistance 66 at contacts 61. However, at this time the outgoing line 50 is closed and the RI drop across coil 58 maintains tube 52 operative to hold relay 55 energized. If the receiving operator opens line 50 to interrupt the sending of the message, tube 52 is rendered inoperative by the shortcircuiting of battery 67 when relay 60 again operates. Relay 55 releases and at contacts 57 opens the incoming line 51. The sending operator is informed of the interruption by the failure of his sounder to respond to the operations of his key. -At contacts 56, relay 55 opens the shortcircuit of battery 71, thereby allowing tube 53 to hold relay 60 operated.

The three modifications of two-way telegraph repeaters shown in Figs. 1, 2 and 3 and described in the foregoing paragraphs are suitable for use with the standard telegraph system having an inductive winding of a relay in series with the line at each of the stations.

Fig. 4 of the drawings discloses a complete telegraph system employing vacuum tubes at the various telegraph stations as well as in the twoway telegraph repeaters. In this figure, S1 represents an end station of the telegraph system, S2 represents a way station of the system, and R is a two-way telegraph repeater circuit. Normally the switches, such as 151 and 152, at all of the telegraph stations will be in closed position.and

current will flow over the telegraph line. With switches 151 and 152 closed, current will flow from the positive pole of battery 104, switch 151, resistance 106, line 101, switch 152, resistance 117,

line 102, armature 137 and its working contact,

resistance 138, to the negative pole of the battery 127. At station S1, the grid of tube 107 is maintained at a positive potential with respect to the filament due to the voltage drop across resistance 106 and sufiicient plate current flows through relay 112 to maintain this relay in operated position. At armature 113 and its working contact, relay 112 maintains the circuit of the sounder 114 closed. Similarly at the way station S2, the grid of tube 118 is maintained at a positive potential due to the voltage drop across resistance 117 and the plate relay 123 is held operated. Relay 123 at armature 124 maintains the circuit of the sounder 125 closed. At the repeater R, the grid of tube 128 is ,maintained at a positive potential due to the voltage drop across resistance 138 and the plate current flowing through repeating relay 130 maintains this relay in operated position and maintains the outgoing line 103 closed. Similarly the normal current flowing over line 103 causes a voltage drop across resistance 139 which maintains the tube 129 operative to hold repeating relay 135 in operated posiat the called station opens tion.

For the purpose of explaining the operation of the system, it will be assumed that a telegraph message is to be transmitted from the end station S1. When the operator at station S1 opens switch 151, preparatory to the sending of the message, current ceases to flow over the telegraph line and since there is no longer an R1 drop across resistance 106 the biasing battery 108 becomes effective to make the grid of tube 107 negative with respect to the filament and stops the flow ofplate current through relay 112. Relay 112 releases and at armature 113 opens the circuit of the sounder 114. Similarly at the way station S2, the interruption of current flow through resistance 117 allows the biasing battery 119 to become effective and place a negative potential on the grid of tube 118. Thisinterrupts the flow of plate current through relay 123 which accordingly releases and at armature 124 opens the circuit of sounder 125.

Referring now to the two-way telegraph re-. peater R, when the line is opened at the sending station, current ceases to flow through the 'resistance 138 and the biasing battery 141 becomes effective to place a negative potential on the grid of tube 128. This interrupts the flow of plate current through relay 130 which accordingly releases and at armature 132 opens the outgoing line 103. At armature 131, relay 130 removes the normal short-circuit from battery 147 and resistance 146 allowing the battery 147 to make the grid of tube 129 positive with respect to the filament of this tube. This is necessary since, when the outgoing line is opened at armature 132, current ceases to flow through resistance 139 and there is no longer a voltage drop across this resistance to maintain the grid of tube 129 at a positive potential. by the positive biasing battery 147 as soon as relay 130 releases and opens its contacts 131. Thus the tube 129 is maintained in operative condition and relay 135 remains operated. At armature 137, relay 135 maintains the incoming line closed, and at armature 136 it maintains the short circuit around resistance 143 and biasing battery 142 associated with tube 128.

Each time key 105 is closed in accordance with the call letters of the wanted station or in accordance with the telegraph message, current flows over the line. At the sending station, the voltage drop across resistance 106 overcomes the effect of battery 108 and places a positive potential on the grid of tube 107. The resulting plate current operates relay 112 which completes the circuit for sounder 114 at contacts 113. Similarly, at station S2 the voltage drop across resistance 117 renders tube 118 operative each time the line circuit is closed, and the resulting plate current operates'relay 1213. Relay 123, at contacts 124, completes the circuit of the sounder 125.

At repeater R, the line current flowing when the sending key is closed causes an RI drop across resistance 138 which overcomes the effect of battery 141 and places a positive potential on the grid of tube 128. The resulting plate current operates relay 130 which repeats the signal over line 103 at contacts 132. At contacts 131 the short circuit around battery 146 is again closed, but at this time the voltage drop across resistance 139 maintains tube 129 operative. When the operator his switch to answer This voltage drop is replaced his station signal or to interrupt at any time during the transmission of the message, tube 129 becomes inoperative as soon as relay 130 is again energized since battery 147 is short-cireuited and there is no voltage drop across resistance 139 as the line 103 is open at thereceiving station. Accordingly relay 135 releases and at armature 137 opens the incoming line. When the key 105, at the sending station 81 is closed in accordance with the. succeeding signals, no current flows over the line and the sounders at the stations fail to respond. The failure of his sounder to respond to the operations of key 105 informs the operator at station S1 that the operator at the receiving station has answered or isinterrupting the message for some reason. He therefore closed his switch 151 and waits to hear from the receiving operator. When relay 135 released it also opened contacts 136 to remove the short-circuit. from battery 142 so that tube 128 became operative to hold relay 130 energized.

The operation of the system for the transmission from line 103 is similar to the above. When line 103 is opened, relay 135 releases and opens line 102 at contacts 137. At contacts 136 the short-circuit is removed from battery 142 which places a positive potential on the grid of tube 128 to maintain this tube operative. Relay 130 is thereby held energized to maintain line 103 closed. At stations S1 and S2, the opening of line 102 stops the current flow through resistances 106 and 117 and the batteries 108 and 119 become effective to stop the flow of plate current through relays 112 and 123. These relays release and open the circuits of the associated sounders 114 and 125.

Each time line 103 is closed by the operation of the key at the sending station in accordance with the telegraph message, relay 135 operates and repeats the signal at contacts 137. At contacts 136, the battery 142 is short-circuited but tube 128 is maintained operative by the voltage drop across resistance 138 and relay 130 is held operated. At stations S1 and S2, the closure of the line results in voltage drops across resistances 106 and 117 which overcome the biasing batteries 108 and 119, respectively, and render tubes 107 and. 118 operative. The plate relays 112 and 123 are operated and complete the circuits of the associated sounders 114 and 125. Assuming that the message is for station S1, the operator at this station may interrupt the transmission of the message at any time by opening his switch 151. The next time relay 135 in the repeater operates to repeat a signal, the battery 142 is short-circuited spond to the operations of the key and he closes his switch and waits to hear from the receiving operator. The receiving operator at station S1 may now operate his key to inform the sending operator of the reason for the interruption.

From the foregoing, it will be apparent that the system permits very rapid signal transmission since the telegraph line contains very little inductance. Thus when the line is closed in accordance with the telegraph signals, the current in the line will practically instantaneously build up to its maximum value since there are no inductive windings in the line which set up counter E. M. F.s to oppose the building up of the current. Similarly, when the line is again opened the current will immediately cease to flow since there is no inductance in the line which opposes the cessation of current iiow.

What is claimed is:

1. In a telegraph system wherein two lines are connected together through a repeater, a vacuum tube associated with each line, and means controlled by each tube for opening the opposite line and maintaining its associated line closed.

2. In a telegraph system wherein two lines are connected together through a repeater, a vacuum tube associated with each line, a relay in the plate circuit of each tube, contacts on each relay for opening the opposite line, and means controlled by each relay for maintaining its associated line-closed.

3. In a telegraph system, two normally closed lines connected together thru a repeater, a vacuum tube associated with each line, said tubes being normally operative, means responsive to the opening of either of said lines for rendering the associated tube inoperative, and means responsive to said last means for opening the opposite line.

4. In a telegraph system, two normally closed lines connected together through a repeater, a vacuum tube associated with each line, said tubes being normally operative, means responsive to the opening of either of said lines for rendering the associated tube inoperative, and means responsive to said last means for opening the opposite line and for maintaining the first line closed.

5. In a telegraph system, two normally closed lines connected together through a repeater, a vacuum tube associated with each line, said tubes being normally operative, means responsive to the opening of either of said lines for rendering the associated tube inoperative, and means responsive to said last means for opening the opposite line and maintaining its associated tube operative.

6. In a telegraph system, two lines connected by a repeater, two vacuum tubes associated with said lines, respectively, two batteries connected in the grid circuits of said tubes, respectively, a plate relay for each tube, contacts on each relay included in the line circuit of the opposite line, and other contacts on each relay for short-circuiting the battery in the grid circuit of the tube associated with the opposite line.

7. In a telegraph system, two lines connected together through a repeater, a repeating tube associated with each line, a plate relay for each repeating tube, contacts on each plate relay included in the opposite line, a holding tube associated with each line, and contacts on each plate relay for rendering the holding tube associated with the opposite line inoperative.

8. In a telegraph system, two lines connected together through a repeater, a repeating tube and a holding tube for each of said lines, a relay connected in the plate circuits of the two tubes associated with the first line, a second relay connected in the plate circuits of the two tubes associated with the second line, and means controlled by each relay for opening the opposite line and for rendering operative the holding tube associated with the opposite line.

9. In a telegraph system, two normally closed lines connected together through a repeater, a normally operative repeating tube and a normally inoperative holding tube associated with each of said lines, means responsive to the opening of one of said lines for rendering its associated repeating tube inoperative, and means responsive to said last means for opening the opposite line and for rendering operative the holding tube associated with the opposite line.

10. In a telegraph system, a telegraph line connecting a plurality of stations, a vacuum tube and a telegraph sounder at each station, a telegraph key and a resistance connected in series in said line at each of said stations, said resistances being connected in the grid circuits of the respective tubes, and a plate relay for each tube for controlling the associated sounder.

11. In a telegraph system, a normally closed crcuit comprising a line, a battery, and a ground return, a plurality of stations each including a vacuum tube and a telegraph sounder, a key and a resistance connected in series in said line at each station, said resistances being connected in the grid c;rcuits of the respective tubes and serving to maintain said tubes operative, means responsive to the opening of said line at any of said stations for rendering all of said tubes inoperative, and means controlled by each tube for controlling its associated sounder.

12. In a telegraph repeater, two lines terminating in a battery, a vacuum tube associated with each line, a resistance in each line included in the grid circuit of the associated tube, a plate relay for each tube, and contacts on each plate relay included in the opposite line.

13. In a telegraph repeater, two lines, a vacuum tube connected to each line, a plate relay for each tube for opening the opposite line, and means controlled by each relay for controlling the grid potential on the tube associated with the opposite line.

14. In a telegraph repeater, two lines, a vacuum tube connected to each line, a normally operated plate relay for each tube, means responsive to the opening of one line for rendering the associated tube inoperative, thereby releasing its plate relay to open the opposite line, and means controlled by said plate relay for preventing the release of the plate relay of the tube associated with the opposite line.

15. In a telegraph repeater, two lines tenninating in a battery, two vacuum tubes connected to said two lines, respectively, a normally operated plate relay for each tube, each plate relay maintaining the opposite line closed, means responsive to the opening of one line for rendering the associated tube inoperative so that its plate relay releases to open the opposite line, and means responsive to the release of said relay for placing a positive potential on the grid of the tube associated with the opposite line to maintain this tube and its plate relay operative, thereby preventing the opening of the first line.

16. In a telegraph repeater, a line, a vacuum tube connected to said line, a normally operated plate relay for said tube, means for opening said line at a distant point to release said relay, means for opening said line at said repeater, and means efiective when said line is opened at said repeater for preventing the release of said plate relay.

17. In a telegraph repeater, a line, a vacuum tube connected to said line, a normally operated plate relay for said tube, means for opening said line at a distant point to vary the potential on the grid of said tube and allow said relay to reline so that the grid lease, means eileotive for controlling the grid that it remains operative operated.

means for opening said .line locally, and when said line is opened locally potential of said tube so to maintain said relay locally for placing a positive potential on the grid of said tube to maintain said relay operated.

19. In a telegraph system, a normally closedline, a station on said line including a resistance in series with the line, a sounder at the station, a vacuum tube having its gridv circuit bridged across said resistance, .a battery in the grid circuit normally tending to provide a negative grid bias, a battery in the line circuit, the voltage drop across said resistance when the line circuit is closed overcoming the voltage of the battery in the grid circuit to provide a positive potential ,on the grid only when the line circuit is closed.

JOHN I. BELLAMY. 

